1. Field of the Invention
The invention relates to the field of molecular gas pumps and may be used for pumping a gas out of microdevices or in analytical microsystems intended for analyzing small volumes of gases, when mechanical movement of a gas becomes inefficient, as well as may be applicable for filtering gases. Also, the invention may be used in the field of indication and express analysis of air for the presence of substances of various kinds, including poisonous substances, chemically dangerous substances, potent toxic substances, as well as may be related to medical equipment, in particular to apparatuses for artificial pulmonary ventilation.
Pumps are used for pumping a gas out of devices which operation requires low vacuum (760 Torr-1 mTorr), high vacuum (1 mTorr-10−7 Torr) or ultrahigh vacuum (10−7 Torr-10−11 Torr). Examples of such devices are mass spectrometers, optical spectrometers, optical electronic devices. Another application for pumps is sampling of a gas from the environment for the purpose of analyzing it in gas detectors and sensors.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Now a trend exists that is directed to reducing instrument dimensions for the purpose of decreasing power consumption, dimensions and weight of devices as well as adapting them for use in microelectromechanical systems (MEMS). Attempts to decrease sizes of existing commonly used mechanical pumps face big problems due to the presence of moving parts in pump designs. A few pump types that exist in a reduced scale now, such as mesoscale pumps and micropumps, exhibit, as a rule, insufficient efficiency and limited applicability, and damage systems with destroying shocks.
One alternative solution is to integrate thermal pumps having no moving mechanical parts and operating due to the effect of gas thermal sliding along non-uniformly heated walls. The claimed device maintains a temperature gradient due to which a directed gas flow is formed during the operation process.
The analogous solution for the claimed device is the classic Knudsen pump consisting of straight, successively connected, cylindrical pipes of small and large radii. Diameters of all pipes of a small radius are similar and many times less than diameters of pipes of a large radius. Thus, the classic Knudsen pump is a periodic structure which period is formed by a pipe of a small radius and a pipe of a large radius that are connected in succession. Temperature distribution is periodical and has the same period, linearly increasing from T1 to T2 along the pipe of a small radius and linearly decreasing from T2 to T1 along the pipe of a large radius. Known technical solutions (U.S. Pat. No. 6,533,554 and US 2008/0178658) present modern implementations of a microscopic Knudsen pump that comprises two thermal baffles having holes for a gas flow, a porous material and a heater. The porous material is an analogue of pipes of a small radius in the classic Knudsen pump. The heater provides for required temperature distribution creating the effect of gas thermal sliding along the walls.
When gas pressures are lower than 0.1 Torr, a length of the gas molecule free run becomes greater than diameters of micropipes; therefore, it is necessary that a pump can be efficiently operated in the free molecular mode formed both in the pipe of a small radius and in the pipe of a large radius. The principal disadvantage of the classic Knudsen pump is that it is insufficiently efficient in this mode. Due to the fact that the pipe shapes are similar, a small pressure relationship is created only on account of different length-diameter ratios of the pipe of a small radius and the pipe of a large radius.
Modern analogues of the classic Knudsen pump are designed in such a way that the free molecular mode exists in pipes of a small radius and the continuous mode exists in pipes of a large radius, i.e., the Knudsen number in pipes of a large radius should be Kn≦0.01. In order to operate a pump at pressures lower than 0.1 Torr, it is necessary to create large-radius pipes of a great diameter which increases pump dimensions significantly and makes it unsuitable for pumping microvolumes of a gas. For example, when the Knudsen number at temperature T=300K is 10 in a small-radius pipe and 0.01 in a large-radius pipe and when a pump may transfer a gas at the pressure of 0.1 Torr, the diameter of large-radius pipes should be 38 mm and at the pressure of 0.01 Torr, it should be equal to 38 cm. Modern designs of pumps use pipes having a diameter not more than 50 microns, which does not enable to efficiently use them at pressures of 0.1 Torr or lower.